The present invention relates to a set of building blocks and, in accordance with the invention, the blocks of such a set are constructed so as to be capable of being held together face to face magnetically.
With this arrangement, when blocks are juxtaposed, face on face, three dimensional figures may be produced, the blocks holding onto one another without dependence on gravity.
The blocks are most simply moulded from plastics material, either solid or hollow.
The magnetic attraction may be provided by magnets, such as bar magnets or transversely polarized magnetic strips, let into the faces of the blocks, or moulded or otherwise provided within the blocks, e.g. fitted to inner surfaces of a multipart moulding before assembly, at positions at which they will provide a sufficient and appropriate magnetic field at the faces of the block.
The positions and/or number of magnetic poles provided for each adjacent face of juxtaposed blocks may be such as to cause particular angular alignment of the faces about an axis perpendicular to the faces. Furthermore, if at least one of those faces has rotational symmetry about an axis perpendicular to the face, the magnetic forces may be such that the blocks will tend to rotate to one or other of a plurality of stable positions corresponding to the symmetry of the face. This may be achieved by providing the rotationally symmetrical face with a pair of opposite magnetic poles on each side of each plane containing the axis of symmetry and one of a number of points of symmetry at the edge of the face, whereby when two of the rotationally symmetrical faces of different blocks are juxtaposed face to face the blocks will tend to rotate relatively to one another to one or other of a plurality of stable positions corresponding in number to the symmetry of the faces. There will thus be provided a ring of alternate magnetic poles around the axis of symmetry arranged symmetrically in pairs. Each pair of poles may be provided by the opposite edges of a transversely polarized magnetic strip which will thus extend on or just below the surface in the radial direction outwardly from the axis of symmetry. By way of example, in the case of a face having the shape of a rhombus, each adjacent pair of quadrants, formed by dividing the rhombus by its diagonals, would contain one a north pole and the other a south pole, for example by two strips of transversely polarized magnetic strip extending end to end, but of opposite hand, down the longer diagonal of the face. It will then be appreciated that if two similar faces are brought together, irrespective of whether or not one face is rotated through 180.degree. relatively to the other, the faces will always be attracted to a stable position in which one rhombic face overlies and is in angular alignment with the other.
The or each rotationally symmetrical face may be provided with a complementary spigot and shallow recess symmetrically one on each side of each plane containing the axis of symmetry and one of a number of points of symmetry at the edge of the face, whereby, in each of the stable positions, opposed spigots and recesses mate with one another. Although the spigots and recesses can be a loose fit, so that they do not hold the faces together, they are useful in inhibiting sliding of the faces over one another under gravity.
The set of blocks may consist of or include two subset each of blocks of the same shape but different from those of the other subset, the blocks of a first one of the subsets having faces with a shape and size which are the same as, or an integral multiple of, those of the faces of the blocks of the second subset, whereby a face of one block, or of each of a number of blocks, of the second subset may be juxtaposed with and attracted to one face of a block of the first subset.
The set of blocks provide particular interest if solid three dimensional bodies can be built by close fitting multiple blocks. Cubic and rectangular parallelopiped blocks are trivial examples and greater interest is provided if the blocks involve angles other than 90.degree., for example subsets of octahedra and tetrahedra. Both the octahedra and tetrahedra may then have edges of common length.
Of greatest interest at the moment is a set of blocks, both subsets of which are formed by rhombohedra, particularly with the blocks of one subset having dihedral angles of 72.degree. (and 108.degree.), and the other having dihedral angles of 36.degree. (and 144.degree.). Each of these two types of rhombohedra will have rhombic faces with an acute angle of 63.43.degree. (the angle whose tangent is 2). In lay terms, each rhombohedron of one subset can be considered to be a cube which has been notionally stretched along a diagonal of the cube, and that of the other subset notionally compressed along the same diagonal. The dihedral angles of 72.degree. and 36.degree. leads to a facinating range of possible interposition of blocks of the two subsets. For example, a possible starting point for a geometric figure involves placing five of the blocks with a dihedral angle of 72.degree. symmetrically around a vertical axis with the edges of the blocks at which the 72.degree. dihedral angle is formed lying parallel to, and immediately adjacent to one another at, the axis. Blocks of both types of subsets can then be close fitted into the recesses formed between the first five blocks. This actually provides a basis, for building a regular triakontahedron, or Keppler's solid, from ten of the blocks of each subset provided all the faces are of the same dimensions.
A set of blocks in accordance with the invention is ideally suited as an educational toy, such as an aid to teaching or for demonstration purposes, involving three dimensional visualization, or as a puzzle. Not only may regular geometric figures, such as quasi-crystals (as defined in Phys. Rev. 1986Series B, Volume 34, pages 596-616), be produced, but the blocks may also be used to produce irregular figures by way of free expression. Three dimensional figures with particularly attractive patterns of blocks may be created if the blocks are of more than one different color. For example, the blocks of one subset may be of one color and those of the other subset of another color.
Although the blocks may be assembled manually, interesting experiments and demonstrations may be carried out if the blocks are of neutral buoyancy in a common liquid, such as water, a salt solution, an oil, or an alcohol, having a specific gravity of between, e.g. 0.5 and 1.5, particularly between 0.8 and 1.1, and, for use in water, 1.0. In that event, in a bath of the liquid, the blocks will automatically and naturally coalesce, owing to the domination of the magnetic forces over gravitational forces, to produce interesting figures. The neutral buoyancy may be provided by making the blocks of a plastics material, such as a foamed plastics material, having a specific gravity less that of the liquid in which the blocks are to be immersed, e.g. in the range of 0.8-0.9 if the liquid is water. The magnetic sources will normally have a specific gravity greater than that of the liquid and the masses of plastics and magnetic materials will be selected so that the overall specific gravity of the blocks is as required, i.e. substantially 1.0 if the liquid is water. A useful development of this principle is obtained if the blocks are suspended in a liquid, such as a variable salt solution, having a vertical density gradient. The blocks will then settle and float substantially at a level corresponding to their own mean density, when the blocks are moulded from a plastics material, they are preferably hollow, rather than solid, as this uses less material and is therefore cheaper and involves less dimensional inaccuracy caused by shrinkage. However, if the hollow interior of a block is sealed and full of air, the mean density of the block is likely to be much less than that of a common liquid. The sealed interior of the block could be filled with a liquid but this would involved potential leakage when the block is not immersed. Preferably therefore, each of the blocks is hollow, and the wall of the block is provided with one or more holes to allow the block to fill with liquid in which it is immersed.
It is not essential for all the faces of all the blocks to attract one another and some may be arranged to repel one another magnetically, or to be quite neutral magnetically, whereby a selection is necessary to achieve an attraction between the adjacent faces of juxtaposed blocks.